The husband, a 41-year-old taxi driver, and his 25-year-old wife were sentenced to two years in prison, but the woman's term was suspended because she is pregnant.
The couple played at Internet cafes on average 10 hours every day and bottle-fed their baby only once a day, prosecutors said in an affidavit.
The girl, who was born prematurely and weighed 5 pounds (2.25 kilograms), was often fed rotten formula and was beaten when she cried out of hunger, the affidavit said.
They found her dead when they returned to their home in Suwon, just south of Seoul, after an all-night gaming session last September, the ruling said. They hid at a relative's home after a autopsy found the baby died of malnutrition.
"This constitutes an inhumane crime where the defendants abandoned even the most basic responsibilities as parents, and is unforgivable beyond any excuse or reason," the Suwon District Court said in the ruling.
The mother will avoid jail time if she stays out of trouble for three years. The couple, who have only been identified by their surnames, Kim, have seven days to appeal.
The case shocked South Korea and raised concern over the severity of online gaming and Internet addiction in the nation of 49 million. The government says there are 2 million "Internet addicts" in the nation considered one of the world's most technologically wired.